This invention relates to a load state detecting apparatus of an induction motor and, more particularly, to a load state detecting apparatus for detecting a load state in an induction motor in accordance with information representing a phase difference between a voltage applied from an alternative power source to the induction motor and a current induced therefrom. The apparatus can be used, for example, as an operation stop control apparatus for controlling interruption of the spin dyring in a washing machine.
The operating duration of an induction motor for driving the bucket in a washing machine during the spin drying is determined by the user, who predicts spin cycle end time in accordance with the amount and type of washing to be done. The user then sets a timer in accordance with the predicted duration. It is, however, difficult to accurately predict the spin drying end time. Inevitably, the user sets a longer time than is necessary. Therefore, operating time is prolonged and power consumption is increased.
For this reason, several techniques have been proposed to automatically set the spin drying time by detecting the load state of the induction motor.
One such technique is to detect induction motor speed. For this purpose, an arrangement using a rotor such as a tachometer is utilized, in which the mechanical movement of the tachometer is converted into an electrical signal. However, this arrangement takes up considerable space and has a short lifetime since mechanically driven members are used. Another conventional technique for detecting the load state of the induction motor uses a simple electrical means for detecting input current to the induction motor. However, the input current varies with external conditions such as power source voltage variations and temperature variations in the induction motor, thus reducing measurement precision.
Therefore, the operation stop control apparatus for controlling spin drying interruption in a washing machine cannot be implemented by simply applying these conventional load state detecting means, since control precision cannot be guaranteed.